This application bases priority on International Application No. PCT/DE00/03574, filed Oct. 11, 2000, which bases priority on German Application No. DE 199 48 997.1, filed Oct. 11, 1999.
1. Field of Invention
The invention relates to an individual blade adjustment system for wind turbines.
2. Description of the Prior Art
For regulating or controlling the generator power, modern wind turbines are often equipped with rotor blades angular adjustment systems. Besides the regulating or control function, the blade adjustment systems still have a safety brake function, in that the rotor blades are set to a large positive or negative angle and, consequently, the rotor produces a brake torque.
The blade angle adjustment systems hitherto known for large wind turbines can be subdivided into electrically and hydraulically operated systems. It is common to all the systems that the rotor blades are mounted at the connection point to the hub by means of an antifriction bearing.
Electrically operated systems generally comprise one geared motor per rotor blade and which by means of the pinion and toothed rim produces a torque at the blade root. The motor can be fixed to the rotor blade and can act in a toothed rim connected to the hub or can be fixed to the hub and act in a rotor blade-side toothed rim on the blade bearing. The electrical supply of the motors takes place by means of slip ring systems. If the slip ring system or the entire power supply fails, the motors are battery-supplied.
Hydraulically operated systems use hydraulic cylinders for blade angle adjustment purposes. In the case of a collective blade adjustment, a single hydraulic cylinder transfers the adjustment forces into the hub and by means of an adjustment mechanism to pivots on the rotor blade roots. Hydraulic individual blade adjustment systems have a hydraulic cylinder for each rotor blade and which acts directly on the rotor blade pivot. The hydraulic pressure is then transferred into the hub by a rotary transmission. If the rotary transmission fails, the hydraulic cylinders are supplied by pressure storage devices in the hub.
Such a hydraulic blade adjustment device is known from DE C2 31 10 263, which describes a hydraulic system which is secure in emergency situations and in which two servodrives act on connecting members articulated by levers. However, the zero position synchronization is complicated. Moreover, to maintain the blade position, it is necessary to have additional mechanically operated locking elements.
In the simultaneously filed application of the same application DE C2 31 10 265, the details of a blade adjustment device are given and which keeps the blades at the same angle, but without preventing the separate operation thereof.
Reference is also made to DE A1 42 21 783, which describes a device for adjusting rotor blades, in which a gear arranged coaxially to the rotor hub with a motor, and by means of a toothed segment link brings about the adjustment of the blades.
Finally, DE A1 198 11 952 describes a method for fixing the rotor blades of a horizontal rotor wind power plant and to a device for performing the method, which is characterized by means for the permanent blocking of a predetermined adjustment angle range of the rotor blades about their longitudinal axis. Said means are formed by an outwardly projecting pawl.
The problem of the invention is to increase the reliability of a blade angle adjustment system. Reliability is essential for the safety of a wind turbine. Otherwise, uncontrollable states can arise where the rotor speed cannot be decelerated by the blade adjustment system.
Therefore, maximum significance is attached to the operational safety and security against failure of such a system. Electrical blade angle adjustment systems suffer from the fundamental disadvantage that in the case of a failure of the power supply, e.g. with a mains failure or cable break, the servomotors have to make do with a power storage device in battery form. They must firstly be switched over to the latter. Therefore, an electrical adjusting system, even in the case of a fault, is dependent on the operation of several electrical components which can be damaged by overvoltages from the mains or lightning strikes, which frequently correspond with power failures.
However, due to the size of the hydraulic cylinders and the geometrical conditions, the hitherto known hydraulic blade adjustment systems require openings in the bearing structure of the rotor hub. Such openings are obviously undesired, because on the one hand they reduce the dynamic loading capacity of the hub, and on the other make difficult or even impossible sealing against entering moisture or saline atmosphere, particularly in the case of offshore wind turbines. The use of an individual hydraulic cylinder for the precise setting of the blade angle, and simultaneously for adjusting large angles in the case of disconnection give rise to compromises in its design to the disadvantage of the setting precision.
This problem is solved according to the invention by the features of the main claim. The subclaims provide advantageous embodiments of the invention.
It is, in particular, advantageous that for improving the regulatability and for reducing the dimensions of a hydraulic blade adjusting system, the regulating and disconnection functions can be separated from one another. A regulating cylinder adjusts the rotor blade only in the angular range necessary for power or speed regulation, whereas, a disconnection cylinder moves the regulating cylinder by means of an adjustment mechanism into the regulating or disconnection position.
In this configuration, the design of the regulating cylinder can be based solely on the regulating function. The shorter travel of the regulating cylinder also leads to a much higher resolution of the necessary path measuring system.
The disconnection cylinder can be designed in an optimum manner for the adjustment function with respect to the adjustment force and speed without having to take account of regulatability.
Another essential advantage of the system is the reduction of the overall dimensions. Through the use of two cylinders, whose arrangement is determined by the geometry of an adjusting linkage, the system can be completely located within the hub so that the latter can be completely enclosed or ventilated in a controlled manner.
In addition, the hub structure can be designed for an optimum force flux because there is no need for openings for the adjustment system.